Determination of Methylarginines in Infant Plasma by CE-LIF.

Methylarginines (MAs) are a class of nitric oxide synthase inhibitors that have been implicated in respiratory complications of critically ill infants. This paper describes the development of an analytical method to measure these compounds in the plasma of newborns using capillary electrophoresis (CE). The CE separation method was optimized to enable complete baseline resolution of the four MA analogues of interest. Sample preparation concerns for infant-derived samples were addressed by validating a heat-assisted extraction method for the analysis of low volume (≤100 µL) samples from a plasma matrix. It was determined that the sample matrix (plasma versus serum) did not affect the measured MA concentrations, while extracting smaller volumes of plasma that underwent heat-induced gelation afforded higher MA recoveries than larger volume samples. These methods were then applied to blood samples collected from infants housed in the neonatal intensive care unit. It was discovered that these newborns had significantly elevated concentrations of MAs at younger ages (< 6 months) while amounts were similar between infants 6 months old and adults. The data are preliminary, but demonstrate an interesting age dependence on the concentrations of these nitric oxide inhibitors, which has not been previously reported.